An Organic Light Emitting Diode (OLED) display is one of hot topics in a research field of a flat panel display. Compared with a Liquid Crystal Display (LCD), the Organic Light Emitting Diode display has advantages of low power consumption, low product costs, self-illumination, broad angles of view, fast response, and so on. Currently, in display devices such as a mobile phone, a Personal Digital Assistant (PDA), a digital camera and the like, the OLED display has gradually replaced the conventional LCD.
A key structure for driving a pixel in the OLED display is a pixel circuit, which includes an OLED and a display driving unit for driving the OLED. The display driving unit is connected with one electrode (anode or cathode) of the OLED. By applying currents having different amplitudes to the electrode, the OLED is caused to display different brightness. Typically, a polarity of the current applied to the OLED by the display driving unit is unchanged, causing the OLED to be offset uni-directionally (in a forward direction or in a backward direction) in long term, and therefore a service life of the OLED is shortened.